简述应急的定义。

青少年学生的安全备受社会关注。在全国中小学安全教育宣传日来临之际, 《21世纪英文报》请你以“How to Keep Us Safe” 为题，写一篇英语短文，谈一谈青少年学生应该如何保障自身的安全。

提示：(1) What should you do at home?

(2) What should you do on the way to school?

(3) What should you do at school?

要求：(1) 短文须包括所有提示内容，可适当发挥。

(2) 文中不得出现真实的人名、校名和地名。

(3) 词数：60～80个。（短文开头和结尾已给出，不计入总词数）

How to Keep Us Safe

Safety is important to us all. As teenagers, we must learn to protect ourselves. ________________________

若x+y=5，则5-x-y=（    ）。

_____ that it was sold out when it came out. [ ]

A. So was her successful book

B. So successful was her book

C. So her book was successful

D. So successful her book was

下面程序执行的结果应是【 】。　　class Test2 {　　　public static void main(String [] args) {　　　int i=2，j=1；　　　byte k=(byte)(i+j)；　　　System.out.println(k)；　　}　}

吗啡作用于脑干极后区、孤束核、迷走神经背核的阿片受体可引起

A．镇痛作用
B．镇咳作用
C．欣快作用
D．胃肠活动改变
E．缩瞳作用